The invention concerns a feed device for a fastening element comprising a positioning piston for positioning a fastening element, a catching clamp for pre-positioning the fastening element for the positioning piston and a housing for holding the positioning piston and the catching clamp, the housing having a feed channel for feeding the fastening element to the catching clamp and the positioning piston being adjustable for positioning the fastening element relative to the housing. Moreover the invention concerns a method for feeding a fastening element.
The reliable feeding of the fastening element to the positioning piston is essential for the automated positioning of a fastening element on a workpiece. Reliable feeding requires accurate pre-positioning of the fastening element. Accurate pre-positioning is particularly difficult if the fastening elements to be positioned are difficult to grasp and might tilt or tip easily.
For example, this is the case if a fastening element such as a rivet or an earthing stud is to be placed on a workpiece, the fastening element being short and thick and having a markedly varying diameter along its length.
Accurate spatial feeding of the fastening element has a role to play during the positioning process e.g. during a welding or soldering process, and influences the type of connection attained. Inaccurate feeding may lead, on the one hand, to faults in positioning the fastening element, which means increased wear on the positioning tool. On the other hand inaccurate feeding may lead to inaccurate positioning and therefore to inaccurate seating of the fastening element, which may require the repeating of the positioning of the fastening element and may be associated with expenditure and costs, particularly if a production method is interrupted.
Therefore the accurate feeding of the fastening element is important for a smooth positioning process and for the quality of the fastening to be attained.
The Gebrauchsmuster DE 296 17 208 U1 describes a stud holder for a stud welding device, where resilient holding fingers of various lengths extend in the longitudinal direction of a stud through-channel and grasp the stud. Because of the spring effect this stud holder is only suitable in the first instance for long narrow studs.
DE 32 18 886 discloses a stud placing machine where a stud is fed via a feed channel to the stud welding device, the stud being held by a stud stop for pre-positioning and the stud being grasped by a stud collet chuck. The stud collet chuck moves the stud in the direction of the workpiece at the same time pushing the stud stop to one side with the stud. There is a risk here that the stud might be moved and tilted spatially by the forces of the stud stop working on it so that, in particular where the positioning piston applies only moderate holding forces, the position of the stud and its axial location are only inaccurately determined.